Convergence of wireless local area networks (WLANs) and third-generation wireless wide area networks will enable mobile devices to roam between a packet-switched network and a circuit-switched network, such as for example, between an 802.11 Wi-Fi network and a public wireless voice/data telecommunications network. This flexibility has inherent advantages, for example, enabling wireless providers to bundle in calls across WLAN spectrum to close gaps in wireless coverage, using the relatively higher bandwidth of the WLAN for data transfers and the relatively lower bandwidth of a wireless air interface such as GSM for voice traffic, extending mobile coverage inside buildings or whenever a user with in range of a WLAN, and providing user access to Voice over Internet Protocol (VoIP) technology to save money or wireless plan minutes. In sum, this notion of wireless convergence promises the ability for an end user to secure an optimal connection to a communications network regardless of the end user's location. Potential applications include domestic services that allow a single access point in a home to serve several handsets that are also used outside the home, and enterprise services that target office environments having a WLAN that serves potentially many access points as well as telephones routed through the office PBX.
To benefit from the advantages of wireless convergence, a mobile device such as a telephone or a Personal Digital Assistant (PDA) must be capable of dual mode or dual network operation. Incoming calls are redirected to dual mode devices regardless of in which network the device is operating, and the dual mode devices then have the ability to handoff between a WLAN and a wireless network as needed. Roaming protocols are required to facilitate handing off between the circuit-switched wireless domain and the packet-switched domain of the WLAN.
Existing and proposed call redirection and handoff solutions disadvantageously must anchor an enterprise-hosted call in the enterprise at all times. For example, the 802.11a based Motorola SCCAN solution provides a proxy engine that controls handoff using two directory numbers and a simple call forwarding protocol that relies on the mobile device and a GSM radio link. Such solutions maintain a first directory number that routes to a wireline network and a second published mobile directory number that is also routable. Expending two directory numbers has the added drawback of complicating or thwarting the provision of a single caller identifier to Caller ID systems. If a call originates from a dual mode device operating in an enterprise network, the first directory number is revealed; if the call originates operating in the wireless network, the second directory number is revealed.